1. Field of the Invention
This invention relates to a fuel injection pump, and particularly to a fuel injection pump having a plunger barrel and a plunger at least one of which is formed with an oil groove for temporarily storing an oil ascending from a cam chamber.
2. Description of Prior Art
A fuel injection pump mainly includes a plunger barrel and a plunger which is reciprocatively slidable along the inner space of the plunger barrel. In the fuel injection pump, a fuel injection to an engine or the like is carried out under pressure through the reciprocative motion of the plunger in the plunger barrel. As well known, a gap between the plunger barrel and the plunger is lubricated by an engine oil or the like in order to carry out the reciprocative motion of the plunger smoothly. In general, the engine oil is stored in a cam chamber disposed beneath the plunger, and it upwardly spreads over the gap between the plunger barrel and the plunger through the reciprocative motion of the plunger in the plunger barrel. If no restriction is imposed on the ascending spread of the oil, the fuel which is supplied to a fuel compressed chamber disposed above the plunger would be finally contaminated by the engine oil. The contamination of the fuel by the engine oil induces various troubles as described later, and thus it is necessary to prevent oil from entering the fuel compressed chamber. one of this type of fuel injection pumps is disclosed in Japanese Laid-Open Patent Application No. 61-123756. In this fuel injection pump, as shown in FIG. 9, the shaft portion of a plunger 103 which is reciprocatively slidable along the inner space of a plunger barrel 101 is formed with an oil groove having a rectangular section on the peripheral surface of the plunger 103.
In the conventional fuel injection pump thus constructed, the oil which is temporarily stored in the oil groove 105 is liable to not only flow downwardly (descend) toward the cam chamber, but also flow upwardly (ascend) toward the fuel side with respect to the position of the oil groove 105 with reciprocative motion of the plunger because the groove shape is rectangular and therefore symmetrical with respect to the upward and downward direction. That is, the conventional fuel injection pump has a disadvantage that the ascension of the oil can not be sufficiently suppressed.
The insufficient suppression of the oil ascension to the fuel side causes the following critical problems. Firstly, it causes the increase of consumption of the engine oil because the engine oil is supplied to the cam chamber. Secondly, as described above, it causes the engine oil to contaminate the fuel which will be supplied to the engine under pressure through the reciprocative motion of the plunger. The contamination of the fuel by the engine oil causes exhaust gas to be discolored. Thirdly, the fuel is injected through a fuel filter to a combustion chamber of an engine under pressure by the plunger, and thus the fuel filter is damaged by the engine oil and the exchange life of the fuel filter becomes shorter if the fuel is contaminated by the engine oil.